People rely on absorbent products, including diapers, feminine pads, dressings for wounds, and adult incontinence articles, to participate in and enjoy their daily activities.
Absorbent products are generally manufactured by combining several components. For disposable absorbent products that are worn by a user, these components typically include a liquid-permeable topsheet; a liquid-impermeable backsheet attached to the topsheet; and an absorbent structure located between the topsheet and the backsheet. When the disposable product is worn, the liquid-permeable topsheet is positioned next to the body of the wearer and allows passage of bodily fluids into the absorbent structure. The liquid-impermeable backsheet helps prevent leakage of fluids held in the absorbent structure. Ideally the absorbent structure has three features: (1) it quickly wicks fluid into the structure; (2) it distributes fluid throughout the structure; and (3) it retains a lot of fluid.
These features can be difficult to simultaneously incorporate into the same structure. Absorption capacity increases when internal void volume in an absorbent structure increases. A higher void volume allows for containment of larger amounts of fluid. Furthermore, an absorbent structure with a higher void volume can better hold multiphasic-fluids containing solids; e.g., menses or feces.
But a higher internal void volume can mean larger pore diameters and a reduced ability to wick fluid into and throughout the absorbent structure.
What is needed is an absorbent structure, and a method of making this structure, that provide both a high absorbent capacity and the ability to wick fluid into and throughout the absorbent structure.
The present invention is directed to an absorbent structure, and a method of making the absorbent structure, that satisfy this need. One method of making a wet-formed composite having latent voids and macro-cavities comprises providing fibers, a dispersion medium for the fibers, and a superabsorbent material swellable in the dispersion medium, the superaborbent material present in an amount of about 10 dry weight percent or less, specifically about 5 dry weight percent or less, and particularly about 2 dry weight percent or less, but more than 0, based on the total dry weight of fibers and superabsorbent material present in the wet-formed composite; thereafter combining the fibers, superabsorbent material, and dispersion medium; forming a wet-formed composite comprising fibers and superabsorbent material, and defining voids between the fibers, from the combination comprising fibers, superabsorbent material, and dispersion medium; providing sufficient contact time between the superabsorbent material and dispersion medium so that the superabsorbent material swells prior to drying the wet-formed composite; drying the wet-formed composite so that the superabsorbent material shrinks, thereby forming macro-cavities between the fibers; and densifying the wet-formed composite to collapse the voids and macro-cavities, thereby forming latent voids and macro-cavities within the densified wet-formed composite; wherein the densified wet-formed composite has a density of about 0.06 grams per cubic centimeter or greater and a basis weight greater than about 100 grams per square meter.
In its dry state, a wet-formed composite of the present invention is suitable for wicking fluids into and throughout the composite. When the wet-formed composite is insulted with fluid, that portion of the composite that is wetted expands as the superabsorbent material swells and latent voids and macro-cavities manifest themselves. This expansion increases internal void volume and absorbent capacity. The portion of the structure that is not yet wetted, i.e. the structure at and beyond the fluid front, remains in its unexpanded form, and therefore suitable for wicking fluids into and throughout portions of the composite increasingly remote from the initial point of fluid insult.
In another aspect, a method of the present invention comprises providing sufficient contact time between the superabsorbent material and dispersion medium before drying the wet-formed composite such that the superabsorbent material swells to at least about 50% of its maximum absorbent capacity, particularly to at least about 75% of its maximum absorbent capacity, specifically to at least about 90% of its maximum absorbent capacity, and more specifically to at least about 95% of its maximum absorbent capacity prior to drying the wet-formed composite. For papermaking processes used to make a wet-formed composite of the present invention, the dispersion medium will generally be a source of water used to operate the papermaking equipment (e.g., city/municipal waterxe2x80x94treated or untreated at the papermaking site, papermaking process water, and the like).
In still another aspect, a method of the present invention comprises providing sufficient contact time between the superabsorbent material and dispersion medium before drying the wet-formed composite such that the superabsorbent material swells by at least about 20 grams, specifically at least about 50 grams, more specifically at least about 75 grams, particularly at least about 100 grams, more particularly at least about 150 grams, and still more particularly at least about 300 grams of dispersion medium per gram of superabsorbent material.
In yet another aspect, the amount of dispersion medium retained in the superabsorbent material after drying is suitably less than about 10% of the superabsorbent material""s maximum absorbent capacity, particularly less than about 5% of the material""s maximum absorbent capacity, specifically less than about 2% of the material""s maximum absorbent capacity, and more specifically less than about 1% of the material""s maximum absorbent capacity.
Other methods of the present invention further comprise the use of materials such as resilient fibers, synthetic fibers, wet-strength agents, dry-strength agents, other additives, and the like, in processes for preparing a wet-formed composite.
In another aspect, methods of the present invention may comprise hydroentangling the newly formed wet-formed composite (i.e., the nascent web).
Another method of the present invention involves making a disposable absorbent article, the method comprising providing a liquid-permeable topsheet, a liquid-impermeable backsheet, and a wet-formed composite defining latent voids and macro-cavities; positioning the wet-formed composite so that it will lie between the topsheet and the backsheet in the disposable absorbent article; and directly or indirectly attaching at least a portion of the topsheet to at least a portion of the backsheet.
Furthermore, the present invention encompasses combining a wet-formed composite having latent voids and macro-cavities with other absorbent structures (e.g., an airlaid structure or the like) to form an absorbent core (e.g., a multi-layer absorbent core comprising the wet-laid composite and the airlaid structure). Alternatively, more than one wet-formed composite of the present invention may be combined to form a multi-layered absorbent core, with each of the plurality of wet-formed composites having the same or different materials and/or properties. Furthermore, a wet-formed composite defining latent voids and macro-cavities may be combined with films, nonwoven webs, and the like to form a multi-layered structure or laminate.
An absorbent structure having features of the present invention comprises a wet-formed composite having interbonded fibers that define latent voids and macro-cavities between the fibers; and superabsorbent material contained by the interbonded fibers, the superabsorbent material present in an amount of about 10 dry weight percent or less, specifically about 5 dry weight percent or less, and particularly about 2 dry weight percent or less, but more than 0, based on the total dry weight of fibers and superabsorbent material present in the wet-formed composite. Wet-formed composites of the present invention have a density of about 0.06 grams per cubic centimeter or greater and a basis weight greater than about 100 grams per square meter.
Wet-formed composites of the present invention may further comprise materials such as resilient fibers; synthetic fibers; wet- or dry-strength agents; other additives; and the like.
In another aspect, wet-formed composites of the present invention are characterized by certain functional properties having recited values or ranges. Examples of such properties include wet:dry cohesive strength, dry internal-cohesion, intake time, Gurley-type stiffness, wicking velocity, and increases in caliper upon wetting (these properties are discussed below).
The present invention also encompasses disposable absorbent articles comprising a wet-formed composite defining latent voids and macro-cavities.
These and other features, aspects, advantages, and versions of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings.